Genetically-encoded fluorescent probe for imaging of oxygenation gradients in living Drosophila

Oxygen concentrations vary between tissues of multicellular organisms and are changing under certain physiological or pathologic conditions. Multiple methods were developed for measuring oxygenation of biological samples in vitro and in vivo. However most of them require complex equipment, are laborious and have significant limitations. Here we report that oxygen concentration determines the choice between two maturation pathways of a DsRed FT (Timer). At high oxygen levels, this DsRed derivate matures predominantly into a red fluorescent isoform. In contrast, a green fluorescent isoform is favored by low oxygen levels. Ratiometric analysis of green and red fluorescence after a pulse of Timer expression in Drosophila larvae provides a record of the history of tissue oxygenation during a subsequent chase period, for the whole animal with single cell precision. Tissue spreads revealed fine differences in oxygen exposure among different cells of the same organ. We expect that simplicity and robustness of our approach will greatly impact hypoxia research at least in small animal models.